'It is a collective fear of aiding radical Islamists that partially informs the Russian public as it supports the Kremlin’s line on Syria.' Photograph: Stringer/Reuters

"Do the people in Russia just not care about dead Syrian children?" "Is everyone over there just a big fan of seeing people gassed inside their homes?" "Do Russians not have souls, or something?" These are just some of the questions I have been asked in the wake of allegations that the Syrian government used deadly chemical weapons against its own people – allegations that the Kremlin continues to mistrust.

On Tuesday, on the eve of the G20 summit in St Petersburg, Russia's President Vladimir Putin gave a rare joint interview to AP and Russia's Channel One, saying that it would have been "absurd" for the government of Bashar al-Assad to use illegal chemical weapons at a time when the Syrian army is "on the offensive". He also said that he "doesn't exclude" the possibility of backing a UN resolution if it is proven that the Syrian government did, in fact, do the "absurd" thing after all.

Putin's statement that Russia will mull over supplying the S-300 air defence system "to certain regions of the world" if the US violates "existing international norms," was read by the interviewers as possibly a veiled threat to supply the S-300s to Iran again.

To get the obvious thing out of the way first: the Kremlin does, indeed, staunchly oppose outside regime change on principle – and opposition to US meddling in the Middle East certainly scores the Russian government plenty of points at home.

The less obvious factor in all of this is the Kremlin's view that Assad, as a state agent, is at the very least a known quantity. It is the Kremlin's view that helping the rebels gain the upper hand in Syria could ultimately lead to more chaos and destabilisation – and, in turn, aid the spread of Islamic radicalism in the region.

Such concerns cannot be dismissed out of hand. Anyone remember the Syrian priest likely killed by rebel group Jabhat al-Nusra? In Russia, much attention was paid to the killing, as well as to the incident in which a rebel cannibalised his enemy.

In the west, we are used to labelling terrorist attacks against western targets as tragedies – but Russian terror victims are often placed in a category apart. Yet terror hurts Russians just as much as it hurts anyone else, and Russian civilians, including moderate Muslims, remain targets for jihadists both in the north caucasus and elsewhere. It is the great collective fear of aiding radical Islamists that partially informs the Russian public as it supports the Kremlin's line on Syria.

The idea I've commonly heard expressed is as follows: the rebels are unpredictable. Many of them are possibly jihadists. If Assad is toppled, what is the guarantee that in the ensuing power vacuum, they will not start slaughtering each other and bringing further destabilisation to the region?

Russians know first-hand that toppling one dictator does not necessarily bring forth democracy and peace – any book on Russian history will tell you that. Russia's bloody, complicated past and its ambiguous present make Russians particularly wary of the sort of idealism that informs Barack Obama's position on Syria.

Older Russians also remember the Soviet Union's invasion of Afghanistan, and how wonderfully that turned out. As for the younger crowd, they have the example of the US invasion of Iraq, something they view as a foolhardy misadventure that ultimately resulted in many, many lives being lost – particularly the lives of Iraqi civilians.

I think it should go without saying that Russians are not stone-hearted barbarians who enjoy seeing bodies of dead Syrian children on TV. But many Russians are also sceptics who have long ago learned that the road to hell is paved with ballistic missiles.

As an ex-paratrooper friend told me recently: "The desire to do something in the face of senseless death is human, it's understandable. But the question you have to ask yourself is, 'can I make things worse?' Do western leaders have a definite answer to that question?"